Levers, such as bicycle cranks or wrenches, use torque to move objects and generally do not create much friction. Increasing the length of a lever usually increases the amount of torque provided when force is applied to the lever. A wrench with a built in ratcheting mechanism is one specific type of lever that allows a person to use a limited range of motion rather than a full rotation needed when using typical wrenches. Because of the limited range of motion needed by ratcheting wrenches, the lever arms can be quite long and therefore provide increased torque. Ratcheting wrenches can also be easier to use because they allow a person to exert a downward force at an efficient angle on the wrench.
Many bicycle cranks are typical levers. Typical bicycle cranks have a moment at 90 degrees (when the crank is up and perpendicular to the ground) where the crank is inefficient at moving the rear wheel because the torque created by the rider's foot is not as great as at other points in the pedaling rotation due to the angle at which the force is applied. Some bicycle cranks, such as rotor cranks, overcome this inefficiency by altering the pedaling motion so that as one crank finishes its downward turn, the other crank has already passed the point perpendicular to the ground, thus providing constant power to turn the rear wheel. Other bicycle cranks, such as the cranks described in U.S. Pat. No. 6,830,259 to Jakovljevic, have a secondary planetary sprocket which extends the effective length of the crank in order to provide more torque.
The information included in this Background section of the specification, including any references cited herein and any description or discussion thereof, is included for technical reference purposes only and is not to be regarded subject matter by which the scope of the invention is to be bound.